This invention relates generally to threaded joints, and more particularly to threaded joints having a visual indication of proper torqueing.
Many types of machinery include threaded joints which must remain secure for safe and proper operation. One example of a common threaded joint are fluid conduit joints using flared coupling nuts (e.g. SAE AS5175), commonly referred to as “B-nuts” in the aircraft industry. Common examples for this type of joint would be fluid lines carrying air, oil, or fuel in a gas turbine engine.
Improperly tightened B nuts are a significant contributor to field leak events and has the potential to create significant consequences such as engine fires and/or in-flight shutdowns. While threaded fasteners torqued under controlled conditions, such as a factory with highly skilled workers, pose very few problems, field repairs may be often carried out by less experienced personnel and/or under sub-optimal conditions.
For example, threaded joints that are typically field accessible (accessories, pipes, etc. that are underneath the external cowling of a gas turbine engine) are routinely repaired in the field. In general, it is not possible to discern if the threaded joint has been properly torqued or if the joint has been torqued at all.